hello, just my motivation is to build faster responsive things when you get old code and remaster it on responsive way … (with css unit like “rem”, “vh”, “vw” ) if firefox can help for that, just easy to make but if i implement with code there are many complexity to add … 
ex: I have
and i want to replace px with vw with no difference in the screen … For me it will save a ton of waste time if it will take 10 sec !!!
else i searching on the web “css px convert to vw” again 
.
whats a drag …